Our objective is to make epidemiologic studies on age-related bone loss, osteoporosis and fractures in female residents of a circumscribed community (Rochester, Minn.). These studies have been made possible by our modification of the dual photon absorptiometry method to permit direct measurement of bone density of the spine and proximal femur (coef. variation is less than 3%) at actual fracture sites, rather than, as has been the case in the past, indirect estimates from measurements of the appendicular skeleton. We plan to apply this methodology to an age-stratified random sample of 300 females to estimate the distribution of bone density levels in the population and prospectively to 200 patients incurring nontraumatic hip or spine fractures. The number of these fractures occurring at each level of bone density will be related to the expected number of women with these levels of bone density in the community population in order to calculate the relative risk of spine or hip fractures at each bone density level. Also, 100 normal female subjects within 20 years postmenopausal will be followed for 4 years with serial measurements to determine rates of bone loss. All subjects having bone density measurements will be interviewed to assess pertinent social, medical, nutritional and behavioral data and will have hormonal and biochemical determinations on blood and urine samples. Serum hormonal determinations will include vitamin D metabolites, immunoreactive parathyroid hormone, immunoreactive calcitonin and sex steroids (including free estradiol and free testosterone). From these data, we will identify those selected variables which best discriminate between women with high and low levels of bone density, women with high and low rates of bone loss and women with and without fractures of the hip and spine. This will permit characterization of those postmenopausal women who are at the highest risk for excessive bone loss and for spine and hip fractures and, therefore, would be candidates for prophylactic therapy. Such information could be used to develop guidelines essential for cost-effective national health care programs to reduce the occurrence of age-related fractures.